Since the year 2021 humanity has been struggling to survive against the outbreak of a parasitic biological agent known as the Gastrea Virus as it ravages the planet. Ten years later Rentaro Satomi of the Tendo Civil Security Agency investigates a Gastrea infection in the Tokyo Area and discovers a mysterious masked man also looking for the infection and stating his goal to destroy the world. Meanwhile Enju Aihara encounters the fleeing infected victim as he grotesquely morphs into a giant Gastrea spider. However as Rentaro and Inspector Tadashima of the Tokyo Police quickly arrive on the scene, Enju makes quick work of the creature when Rentaro weakens it with his black Varanium bullets. Afterwards Rentaro delivers his mission report to his superior and friend Kisara Tendo despite receiving a severe scolding for prioritizing food over receiving the company's payment for assisting the Tokyo Police. However with the source of the recent Gastrea infection still elusive, Rentaro pays his teacher, Sumire Muroto a visit and leans that it may be using a camouflaging ability to avoid detection. The next day after dropping Enju off at school, Rentaro reflects on humanity's status in the war against the virus and their last hope for survival: the Cursed Children.